U.S. patent number 5,261,517 [Application Number 07/900,208] was granted by the patent office on 1993-11-16 for multi-disk clutch.
This patent grant is currently assigned to Deere & Company. Invention is credited to Hubert Hering.
United States Patent |
5,261,517 |
Hering |
November 16, 1993 |
Multi-disk clutch
Abstract
A multiple disk clutch has a clutch disk stack which is pressed
together by a spring arrangement and released by a fluid pressure
operated piston which is movable against the force of the spring
arrangement. To provide a low cost clutch with fewer parts, the
clutch disk stack is placed in an essentially sealed chamber which
can be pressurized by a pressure source. One side of the chamber is
closed by the piston. The chamber therefore serves both as the
clutch disk stack chamber and the piston pressure chamber. If the
pressure in the chamber increase, the piston moves against the
spring and releases the plates. If the pressure in the chamber
decreases, the clutch plates are pressed back together by the
spring.
Inventors: |
Hering; Hubert (Kirchheim,
DE) |
Assignee: |
Deere & Company (Moline,
IL)
|
Family
ID: |
6434088 |
Appl.
No.: |
07/900,208 |
Filed: |
June 17, 1992 |
Foreign Application Priority Data
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Jun 17, 1991 [DE] |
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4119874 |
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Current U.S.
Class: |
192/85.37;
192/56.2; 192/70.27 |
Current CPC
Class: |
F16D
25/123 (20130101); F16D 25/0638 (20130101) |
Current International
Class: |
F16D
25/06 (20060101); F16D 25/12 (20060101); F16D
25/00 (20060101); F16D 25/0638 (20060101); F16D
025/06 () |
Field of
Search: |
;192/91A,57,58C,85CA,85AA,70.27 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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224680 |
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Apr 1959 |
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AU |
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0365794 |
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May 1990 |
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EP |
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1286836 |
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Mar 1969 |
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DE |
|
1475499 |
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Jun 1969 |
|
DE |
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1675242 |
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Feb 1971 |
|
DE |
|
2042289 |
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Mar 1972 |
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DE |
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3605004 |
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Aug 1986 |
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DE |
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1518672 |
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Mar 1968 |
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FR |
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2583479 |
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Dec 1986 |
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FR |
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2633024 |
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Dec 1989 |
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FR |
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46-21523 |
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Jul 1968 |
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JP |
|
586385 |
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Mar 1947 |
|
GB |
|
1483860 |
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Aug 1977 |
|
GB |
|
85/05660 |
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Dec 1985 |
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WO |
|
Primary Examiner: Braun; Leslie A.
Assistant Examiner: Pitts; Andrea
Claims
I claim:
1. A multi-disk clutch comprising:
a. a clutch drum having a recess formed therein;
b. a clutch hub substantially within said clutch drum recess;
c. a shaft to which said clutch hub is fixed for rotation and about
which said clutch drum is rotatably mounted;
d. a piston substantially within said clutch drum recess, said
piston and said clutch drum recess substantially defining a chamber
therebetween;
e. a first plurality of disks within said chamber and fixed for
rotation with said clutch drum;
f. a second plurality of disks within said chamber, fixed for
rotation with said clutch hub, and interleaved between and
selectively engageable with said first plurality of disks;
g. spring means biasing said piston to move said first and second
plurality of disks into engagement with each other;
h. control means for selectively providing a pressurized medium to
said chamber to press said piston away from said first and second
pluralities of disks to allow said disks to disengage, said control
means comprising:
1) at least one axial bore and at least one generally radial supply
bore formed in said shaft connecting said chamber with said axial
bore to provide a passage to supply said pressure medium to said
chamber;
2) a reservoir for said pressure medium; and
3) valve means for connecting a radially outward region of said
chamber to said reservoir when said clutch is engaged.
2. The multi-disk clutch of claim 1, wherein said clutch drum and
said piston each have radial surfaces between which said disks are
compressed when said piston presses said disks together.
3. The multi-disk clutch of claim 1, wherein said spring means
comprises a compression spring located in said clutch drum recess
on a side of said piston outside of said chamber, and means for
holding one side of said compression spring axially fixed relative
to said clutch drum with the other side of said compression spring
pressed against said piston.
4. The multi-disk clutch of claim 1, wherein surfaces of said
clutch drum and said piston acted upon by said pressure medium have
substantially the same surface in area.
5. The multi-disk clutch of claim 1, wherein said valve opens and
closes based upon the pressure of said pressure medium, and wherein
said valve closes at a pressure lower than the pressure necessary
to move said piston away from said disks sufficiently to allow said
disks to disengage.
6. The multi-disk clutch of claim 1, wherein said disks have axial
penetrations and grooves formed therein to enhance flow of said
pressure medium.
7. The multi-disk clutch of claim 1, further comprising sealing
means for hermetically sealing said chamber when said clutch is
engaged, and wherein said pressure medium has a vapor pressure such
that it will build sufficient pressure in said chamber when a
predetermined temperature is exceeded to move said piston away from
said disks sufficiently to allow said disks to disengage.
8. The multi-disk clutch of claim 1, wherein a portion of said
clutch drum generally surrounding said disks has penetration
openings formed therein, said penetrations being of a size that
they act as throttling restrictions that permit a pressure build-up
in the chamber when said clutch is disengaged, yet permit passage
of a flow of coolant adequate to cool said clutch when said clutch
is engaged.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a multi-disk clutch of the type having
layered clutch disks that can be pressed together by a spring
arrangement to engage the clutch and a piston that can be actuated
by a pressurized medium to move against the spring force to
separate the clutch disks from each other.
2. Description of the Related Art
Multi-disk clutches are typically biased either into or out of
engagement by a spring arrangement, then moved out or into
engagement by using pressurized oil or air in a piston chamber to
press a piston against the force of the spring. Such clutches often
are used in agricultural and industrial vehicles, such as
agricultural tractors and the like, to control the front wheel
drive. For safety reasons in this situation, the stack of clutch
disks is loaded by a spring arrangement so that the clutch is
engaged when the clutch piston chamber is de-pressurized and
disengaged when the piston chamber is pressurized.
In addition to the clutch disks, clutches of this type contain
pressure plates that cover the stack of clutch disks on either
side, some mechanism for transmitting the force of the piston to
the spring arrangement and other auxiliary devices. Typically, a
pressure plate supports the clutch drum side of the stack of clutch
disks, while the spring engages the other side of the stack. Of
course, all of these various components increase the cost of
producing the clutch.
SUMMARY OF THE INVENTION
It is the object of the present to provide a low cost multi-disk
clutch, and in particular, one in which the number of components is
to be reduced, with the remaining components performing added
functions.
This object is achieved according to the present invention by
locating the clutch disks in a generally sealed chamber, which is
enclosed on at least one side by a piston, and in which the chamber
can be connected to a source of pressure medium. The disk chamber
thereby simultaneously serves as the piston chamber, and the
pressure medium for the piston simultaneously can be used as the
cooling medium for the clutch disks.
This structure eliminates pressure plates and auxiliary devices to
transmit the force of the piston to the spring arrangement, since
the mechanism for disengaging the clutch has been integrated into
the space for the clutch disks. The number of parts therefore is
reduced, resulting in a cost effective design that is compact and
nevertheless allows cooling oil to flow through the stack of clutch
disks.
The pressure medium is preferably an incompressible fluid such as
pressurized oil, although in principle such a clutch can also be
designed for compressed air.
Preferably, the clutch disks are a stack of disks arranged between
a radial surface of the housing enclosing the chamber and a radial
surface of the piston. Thus the piston itself serves as the clutch
pressure plate, and separate clutch pressure plates are not
required.
A simple embodiment for the spring arrangement is to have the side
of the piston external to the chamber engage a compression spring,
which may be a Belleville spring whose inner or outer edge is
supported against the housing or clutch drum.
To avoid axial forces between the clutch components and the clutch
shaft due to the pressure load in the chamber, the surfaces of the
piston and the clutch drum affected by the pressure medium should
preferably be designed to have the same surface areas.
It is advantageous to supply the pressure medium through an axial
bore in the clutch shaft, with at least one supply bore connecting
the chamber with the axial bore, where the pressure can be
controlled by a control valve. Most appropriately, several supply
bores can be distributed over the axial extent of the stack of
clutch disks. This allows the pressure medium to spread rapidly
through the entire chamber and penetrate between the clutch disks,
so that the disks can more easily separate from each other. Axial
bores may also be provided in the clutch disks to further aid this
process. Such bores preferably are provided in the inner disks
which are connected with the shaft, in particular in the area that
lies radially outward of the set of gear teeth between the clutch
hub and the shaft.
To improve the penetration of the pressure medium between the
clutch disks, there is a further advantage in providing grooves
generally radial in the surface of the clutch disks. The grooves
also should be relatively narrow to avoid an excessive reduction in
the disk lining. The pressure medium then can spread across the
friction surfaces and contact surfaces of the clutch disks, helping
the clutch disks separate from each other whenever a certain
pressure in the clutch disk chamber is reached and the piston is
moved against the spring load to disengage the clutch.
High loads on the clutch can result in the clutch disks slipping
with respect to each other, even when the clutch is engaged. This
carries with it the danger that the temperature of the clutch disks
rise due to friction after only a short time, and that the disks
might be damaged.
Accordingly, a further embodiment of the invention provides for
cooling of the clutch disks when the clutch is engaged by providing
a valve through which a radially outward region of the chamber can
be connected to a reservoir for the pressure medium when the clutch
is engaged. This valve allows flow of the pressure medium
(simultaneously used as a cooling medium) through the stack of
clutch disks even when the disks are engaged. However, the valve
preferably closes the outlet to the reservoir when the chamber is
pressurized.
A convenient design for the valve is to have it controlled by the
pressure of the medium in the chamber, so that it closes the
connection to the reservoir at a pressure that is below that
necessary to separate the disks from each other. The closing
pressure should be low, if possible, for example, one tenth of the
system pressure, so that not too much pressure medium flows through
the connection into the reservoir when the clutch is disengaged. A
high closing pressure would also require a high spring force for
the spring arrangement. At the same time, the cross sectional area
of the connection between the chamber and the reservoir should be
designed so that adequate cooling flow is assured despite the
relatively low pressure difference.
Alternatively, or in addition to this valve, outlet openings for
the pressure medium can be provided in the outer surface of the
clutch drum surrounding the clutch disks, dimensioned in such a way
that they throttle flow and permit a pressure buildup in the
chamber during clutch disengagement, yet permit adequate cooling
flow when the clutch is engaged. To cool the clutch when it is
engaged, the cooling flow is maintained by the centrifugal forces
existing in the chamber and/or by a relatively small excess
pressure in the chamber which is retained when the clutch is
engaged.
The multi-disk clutch according to the invention can also be
designed to great advantage as safety clutch in which the clutch
disks separate from each other upon excessive heating and thereby
are protected against damage. The chamber in which the clutch disks
are located remains largely sealed even when the clutch is engaged,
so that the pressure medium cannot escape from the chamber quickly.
If heating in the stack of clutch disks occurs due to a process of
slipping when the clutch is engaged, then the pressure in the
chamber will increase according to the vapor pressure
characteristic of the pressure medium. If the pressure in the
chamber exceeds the opposing pressure generated by the spring
arrangement, then the piston will move, the clutch disks will
separate and torque transmission will be interrupted. Any further
heating of the clutch disks will be avoided. The release point of
the clutch can be controlled by appropriate design of the clutch
and selection of the pressure medium.
Due to the extensive sealing of the chamber required for it to
function as a pressure chamber, coolant flow generally is limited.
Hence the multi-disks clutch according to the invention is
preferably applied in situations in which relatively low friction
power must be transmitted or where low relative rotational speeds
occur between the shafts to be connected when the clutch is
disengaged. This is the case, for example, between differential
gear boxes of passenger vehicles as well as in front axle clutches
and differential locking clutches.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in greater detail with
reference to the drawings, in which:
FIG. 1 shows a cross section of a first embodiment of a multi-disk
clutch according to the invention; and
FIG. 2 shows a cross section of a second embodiment of a multi-disk
clutch according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a shaft 12 is supported in tapered roller
bearings 14, 16 in the clutch housing 10. The pressure/cooling oil
collects in the clutch housing 10, which acts as a reservoir. The
shaft ends are sealed by seals 18, 20 against the clutch housing 10
or a bearing cover 22.
In its central region, the shaft 12 carries a set of gear teeth 24
that mesh with the inner disks 26 of a stack of disks 28. The outer
disks 30 of the stack of disks 28 mesh with a set of gear teeth 32
of a clutch drum 34.
The clutch drum 34 acts as a housing for the stack of disks 28 and
is supported by journal bushings 36, 38 on the shaft 12, free to
rotate, and is secured against axial movement by a contact washer
40. A drive gear 44 is attached to the clutch drum 34 by screws 42
and meshes with an output gear of a vehicle gearbox, not shown.
A piston 46 is arranged in a cylindrical recess 45 of the clutch
drum 34 so as to be axially movable but fixed against rotation. The
piston 46 is sealed by an O-ring 48 against the clutch drum 34 and
by a seal 50 against the shaft 12. The seal 50 is designed to
accommodate rotational as well as axial movements. A further seal
51 seals the shaft 12 with respect to the clutch drum 34.
The clutch drum 34, the shaft 12 and the piston 46 enclose a
generally sealed chamber 52 that contains the stack of clutch disks
28. The stack of disks 28 is in contact on one side with a
ring-shaped projection of the clutch drum 34 and on its other side
with a ring-shaped projection of the piston 46. Separate pressure
plates need not be provided.
A Belleville spring 54 lying outside the piston 46 but inside the
recess 45 of the clutch drum 34 has an outer edge supported by a
retaining ring 56 that engages the clutch drum 34 and an inner edge
preloaded against the exterior surface of the piston 46, so that
the piston 46 is pressed against the stack of disks 28 to compress
it. When the stack of disks 28 is compressed, the clutch is engaged
and transmits torque from the input gear 44 through the clutch drum
34 to the shaft 12. The preload of the Belleville spring 54 is
selected so that a predetermined torque is transmitted without the
disks 26, 30 slipping with respect to each other.
The shaft 12 is provided with an axial bore 58 as well as radial
supply bores 60, only two of which are shown. The supply bores 60
connect the axial bore 58 with the chamber 52. The axial bore 58 is
connected through a housing bore 62 with a hydraulic supply system
64. The latter is formed generally by a hydraulic pump 66, a valve
68 and a reservoir 70. The pump 66 delivers the system pressure,
for example, 12 Bar. The valve 68 shown is an electromagnetic
three-way control valve with three positions, which can be moved
from its first position as shown by an electric control signal
against the force of a spring 72. The degree of movement depends
upon the magnitude of the electric control signal.
In the first position (illustrated), the valve 68 connects the
outlet of the hydraulic pump 66 with the chamber 52. In this
position the valve 68 contains a throttling restriction 74 so that
the system pressure of the pump 66 is reduced, for example to
approximately 1 or 2 Bar. This pressure is not sufficient to move
the piston 46 against the force of the Belleville spring 54 towards
the outside (which would release the disks 26, 30 from one another
to disengage the clutch). However, it is sufficient to cool the
stack of disks 28, as will be described below.
In a second, central position of the valve 68, the chamber 52 is
connected with the reservoir 70, so that the pressure in the
chamber 52 is released and the clutch is engaged.
In a third position, the valve 68 connects the outlet of the
hydraulic pump 66 with the chamber 52 without interposing any
significant throttling. This increases the pressure in the chamber
52 to the system pressure and results in the piston 46 moving
outward against the force of the Belleville spring 54. The disks
26, 30 then can rotate with respect to each other, disengaging the
clutch and halting transmission of any torque.
A generally radial channel 76 is located in the clutch drum 34 to
connect a corresponding channel 78 and the axial bore 58 in the
shaft 12 with the outer contour of the clutch drum 34. The outer
region of the channel 76 also is connected by a cross channel 80
with the radially outward region of the chamber 52. A movable valve
82 is arranged in the channel 76 which can close the opening
between the cross channel 80 and the channel 76. The valve 82 is
loaded by a spring 84 to bias the valve 82 radially inward to its
open position.
With the valve 82 in its open position, coolant flow is possible
from the pump 66 through the valve 68, the bore 58, the supply
bores 60, the chamber 52, the cross channel 80 and the radial
channel 76 to the reservoir in the clutch housing 10. As a result,
coolant flow is maintained when the clutch is engaged, which
protects the clutch disks 26, 30 from overheating if the clutch
disks 26, 30 slip with respect to one another due to an
overload.
To disengage the clutch, the electromagnetic coil of the valve 68
is energized to move the valve to its third position. This supplies
the full system pressure of the hydraulic pump 66 to the chamber 52
without any throttling. This also simultaneously moves the valve 82
radially outward against the force of the spring 84 due to the
pressure in channel 76 and closes the cross channel 80, thereby
avoiding a pressure drop in the chamber 52. Hence no cooling is
performed on the stack of clutch disks 28 when the clutch is
disengaged, when cooling would be superfluous.
If the clutch is again to be engaged, the electromagnetic coil of
the valve 68 is de-energized so that the valve 68 returns to its
first position. In doing so, it passes through its center position,
in which the chamber 52 is connected with the reservoir 70 and its
pressure quickly released. The valve 68 is so designed that it
remains in this center position for a period of time that is
adequate to reduce the pressure in the chamber 52 and the bore 58
completely. This pressure reduction also allows reopening of the
valve 82 due to the influence of the spring 84, opening the cross
channel 80.
Instead of or in addition to using the valve 82 to maintain coolant
as shown in FIG. 1, flow can be maintained by providing relatively
narrow bores 88 in the circumference of the outer cylinder surface
of the clutch drum 34. Fluid then can be continually ejected from
the chamber 52 through these bores 88 due to centrifugal force or
the pressure supplied by the hydraulic system 64. The bores 88 must
be sufficiently large to assure an adequate flow of coolant, yet
not large enough to lead to an unacceptably high pressure drop in
the chamber 52 when the clutch is disengaged.
FIG. 2 illustrates an alternative embodiment of the present
invention. Most of the elements in FIG. 2 are identical to those in
FIG. 11, have been identified with the same reference numerals, and
will not be further described herein.
In the multi-disk clutch of FIG. 2, the chamber 52 is hermetically
sealed from the outside and is connected to a hydraulic system 92
only by the radial supply bores 60, the axial bore 58 and the
housing bore 62. Channels 76, 78, 80 and 88 have been omitted. The
hydraulic system 92 differs from the hydraulic system 64 shown in
FIG. 1 in that the valve 94 completely interrupts fluid flow from
the hydraulic pump 66 to the chamber 52 when it is in its first
position. In this valve position, fluid can neither be supplied to
the chamber 52 nor drained from the chamber 52. If the clutch is
overloaded, the disks 26, 30 will overheat, in turn heating the
pressure medium in the chamber 52. As the temperature of the
pressure medium rises, the pressure in the chamber 52 will increase
in accordance with the vapor pressure characteristic of the
pressure medium. If the pressure rises above the opposing pressure
generated by the Belleville spring 54, the piston 46 will move to
the left and the clutch disks 26, 30 will separate. This protects
the clutch from damage due to overheating.
In either of the above embodiments, the inner disks 26 may be
provided with cross bores 86 in their radially inward region to
assure good pressure equalization in the chamber 52. In addition
the surfaces of the disks 26, 30 that carry the clutch lining may
be provided with generally radial grooves through which fluid can
penetrate between the disks 26, 30, so that pressure equalization
occurs between the disks 26, 30. Furthermore the grooves allow
fluid to flow from their radially inward to radially outward sides,
helping maintain a flow of coolant, even when the clutch is
engaged.
While the invention has been described in conjunction with a
specific embodiment, it is to be understood that many alternatives,
modifications and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, this
invention is intended to embrace all such alternatives,
modifications and variations which fall within the spirit and scope
of the appended claims.
* * * * *